40Cr steel round bar is a medium-carbon, chromium-alloyed quenched-and-tempered steel widely used for shafts, gears, spindles and structural machine parts where a balance of strength, toughness and good hardenability is required. For buyers seeking reliable supply from China at factory prices and fast lead times, MWAlloys offers mill-direct 40Cr round bars (full traceability, factory pricing, and steady stock for common diameters).

What is 40Cr steel?

Definition & role.
40Cr is a medium-carbon chromium alloy steel under the Chinese GB/T 3077 family (often supplied in hot-rolled or forged round bars). It is designed to be quenched and tempered to obtain a combination of tensile strength, toughness and wear resistance. In global nomenclature it is commonly cross-referenced to AISI/SAE 5140, DIN/EN 41Cr4 / 1.7035, and JIS SCr440.

Brief history & practical note.
This grade evolved to meet the need for components that must be stronger and more hardenable than plain carbon steels (e.g., 45/1050), while remaining cost-effective compared with more highly alloyed steels. It is widely stocked as round bar and forged blanks and is a go-to choice for mid-duty shafts, gears and linkages.

Chemical composition — standard ranges

Below is a concise table with the commonly accepted chemical composition ranges used by major standards (GB/T, ASTM/SAE, EN/JIS). Small differences occur by standard and by supplier; always verify the mill certificate (MTC).

(Sources and consolidated standard ranges.)

Commentary on chemistry:

• Carbon controls core strength and hardenability; 40Cr sits in the medium-carbon range.

• Chromium (≈0.8–1.1%) increases hardenability and wear resistance without drastically reducing weldability.

• Silicon and manganese are deoxidizers and contribute to strength.
  Always accept supplier certificates and spectro reports when chemical composition is critical for your application.

Material properties — mechanical & physical

The properties below reflect typical guaranteed ranges for quenched & tempered or normalized conditions from mill datasheets and standards. Exact properties depend on heat treatment, section size and supplier.

Mechanical properties (typical / guaranteed ranges)

(Representative datasheet ranges — confirm with MTC for a specific heat and temper.)

Physical properties (approximate)

• Density: ≈ 7.85 g/cm³ (7,850 kg/m³)

• Young’s modulus: ≈ 210 GPa

• Thermal conductivity and expansion are similar to other medium-carbon steels.

40Cr steel round bar specifications — sizes, tolerances, delivery conditions

Common supply forms. Round bars supplied hot-rolled, normalized, annealed, bright/turned (cold drawn) or quenched & tempered; typical length 3–12 m (cut lengths available). Mills commonly mark with heat number and supply an MTC.

Typical dimensional range (examples):

• Diameters commonly stocked: 18 mm — 320 mm (small-dia machining bars to large forgings). Suppliers can offer custom diameters and lengths.

Tolerances & finish:

• Hot-rolled black bars have wider tolerances; bright/turned bars meet tighter tolerances for machining.

• Surface conditions: black, turned, ground, or bright; ends usually sawed and bar ends identified with heat no.

Metal forming & heat-treatment processes for 40Cr round bars

40Cr responds well to common steel fabrication and heat-treatment methods. Below is a practical overview.

Primary metalworking routes

• Hot rolling / forging — primary shaping for bars and blanks; typical forging temperatures 1100–850 °C.

• Cold drawing / turning (bright finish) — improves surface, straightness and dimensional tolerance for smaller diameters.

• Machining — 40Cr is machinable in annealed or normalized state; machinability drops when hardened. Carbide tooling recommended for hard conditions.

Heat treatment (key cycles and targets)

• Annealing (softening): heat to ~680–720 °C, slow cooling to reduce hardness (→ ≤ 207 HB). Used to improve machinability.

• Normalizing: 840–880 °C, air cool — refines grain and improves toughness.

• Hardening (quench): austenitize roughly 820–860 °C, quench (oil typical) — produces martensitic structure. Quench severity depends on section thickness.

• Tempering: usually 520–680 °C depending on target hardness/toughness; higher tempering temperatures yield lower hardness but better toughness.

Surface hardening:

• 40Cr is well suited to induction or flame hardening and also responds to carburizing if higher surface hardness is required (but 40Cr is not a dedicated case-hardening steel—choose the right alloy if deep case is required).

International equivalents (quick cross-reference)

How to use cross-references: equivalents are close but not identical; always confirm composition and mechanical specs before substitution, especially for critical or safety parts.

What 40Cr round bar is used for

Common applications where 40Cr round bar is chosen:

• Shafts and axles (driveshafts, transmission shafts) — good balance of strength and toughness.

• Gears and splines (medium duty) — can be case-or surface-hardened.

• Mechanical couplings, studs and pins — where moderate wear resistance is needed.

• Tooling components for medium wear loads (jigs, fixtures).

• Automotive parts — steering knuckles, rear axle components, etc.

Selection tip: For parts subject to high cyclic load or fatigue, prefer properly heat-treated 40Cr with controlled grain size and NDT, or a higher-alloy grade if environment and duty demand it.

40cr Steel Bars Sizes & weight

Weight formula (metric):
Weight (kg/m) ≈ 0.006165 × D², where D is diameter in mm. (Engineering Toolbox uses a rounded constant 0.00617 or 0.0062 depending on units). For common use we use: W(kg/m) = 0.00617 × D(mm)².

Example diameter → weight per metre (rounded):

(Use the formula above for intermediate sizes; verify with supplier weight charts for exact shipping calculations.)

40CR Steel Bar Price comparison

Important note on price transparency: steel prices vary rapidly with raw materials, freight, quantity, surface finish, tolerances, and contractual terms. The numbers below are market snapshot ranges for 40Cr/5140 alloy round bar as of 2025 (illustrative; verify quotes from mills or authorized distributors). Sources are live supplier listings and market price indices — ranges overlap because suppliers sell different quantities (small orders retail vs. mill lots).

Why the ranges are wide

• Small order retail vs. direct mill FOB bulk orders.

• Finish: bright/ground/turned bars cost more than black hot-rolled.

• Heat treatment / certification (full MTC, PMI, NDT) adds cost.

• Global logistics and duties influence landed cost.

How MWAlloys positions price & lead time
MWAlloys works with Chinese mills and keeps stock for common diameters; we quote 100% factory price for bulk orders and can typically ship stock items faster than brokers — contact for live FOB/FOB+logistics quotes (lead time depends on quantity and spec).

Quality, testing and what to request from suppliers

When purchasing 40Cr round bars, ask for:

1. Mill Test Certificate (MTC / EN 10204 3.1 or 3.2) — mandatory for critical components.

2. Chemical analysis report — spectro reading for each heat.

3. Heat treatment chart — the austenitizing temp, quench medium, temper temperature.

4. NDT (ultrasonic / magnetic particle) results for critical forgings or large diameter bars.

5. Hardness test results (Brinell/HRC) and tensile test (if required).

6. Traceability & heat no. on each bar (important for warranty and failure analysis).

Additional tests for special service: fatigue testing, metallographic grain size, and coating/adherence testing (if plated or coated) are available on request from reputable mills.

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